Project Summary/Abstract Lung cancer remains the leading cause of cancer-related death worldwide. While advances in identification of key drivers and corresponding targeted therapies have improved the outcome for specific subclasses of non- small cell lung cancer (NSCLC), they are ultimately ineffective; thus, there continues to be a need for the identification of novel therapeutic targets. Most targeted therapies currently in use are directed at specific proteins corresponding to genes mutated in lung cancer. However, tumor cells also receive pro-growth signals from the tumor microenvironment (TME), providing another possible avenue for anti-cancer therapy. If communication between epithelial cells and their underlying stroma is aberrantly regulated, their interactions can prove to be tumorigenic. Although cancer-associated fibroblasts (CAFs) are known to promote and sustain the growth of tumors, the underlying mechanisms remain incompletely understood, and expanding the lung cancer therapeutic armamentarium by blocking tumor-stroma interactions could serve as a yet unexplored approach to the treatment of lung cancer. Importantly, since this approach is not based on blocking a specific oncogenic mutation, it may have beneficial effects across NSCLC with a variety of genotypes. Previous work in our laboratory identified a novel mechanism of tumor-stroma signaling: CAFs secrete CLCF1, a cytokine that binds CNTFR on tumor cells and promotes neoplastic growth. Through a collaboration with the laboratory of Dr. Jennifer Cochran (Stanford), we have developed an engineered ligand decoy to block CLCF1- CNTFR signaling (eCNTFR). My long-term goal is to identify novel strategies to treat NSCLC. My central hypothesis is that CAF-tumor signaling, and particularly CLCF1-CNTFR signaling, is critical for tumor progression in NSCLC. More specifically, I will test the hypothesis that CLCF1 blockade is an effective therapeutic strategy in NSCLC and that the mechanism of action is related, at least in part, to differentiation of tumor cells towards a more epithelial and less mesenchymal phenotype. Completion of the following specific aims should test the central hypothesis and, thereby, attain the objective of this application. Specific Aim 1: To test the efficacy of a novel engineered CNTFR (eCNTFR) decoy in treating NSCLC using use both cell line and patient-derived tumor xenograft models as well as genetically-engineered mouse models. Specific Aim 2: To characterize the downstream pathways involved in CLCF1-CNTFR signaling and their role in tumor progression using biochemical and genomics approaches. Successful execution of the work described will result in greater understanding of the mechanisms underlying tumor progression in lung cancer. This contribution will have broad impacts: (1) identifying for the first time a critical role for CLCF1-CNTFR signaling in NSCLC progression; (2) elucidating the downstream pathways involved in the CLCF1-CNTFR signaling axis; (3) increasing our knowledge of tumor-stroma signaling in oncogenic contexts; and (4) facilitating the development of a novel therapeutic strategy in NSCLC.